I was part of a team that ran a LARP this weekend. There were certain types of action that we thought were undesirable for the style of game we were trying for, so we just didn’t provide a way to do them. This works in a board game, but when a roleplayer wants to do something that the rules do not provide for, it is frustrating and no one knows quite what to do.
What I wish we had done is provided a way to resolve the activity in question, but in as un-fun a way as possible. Players often want to do impossible things, but dull things usually get a pass. This was why my Vampire LARP, back in the day, used Mind’s Eye Theatre despite its many flaws: combat was so dragged-out and unpleasant that it was an effective deterrent for combat in any situation that didn’t absolutely demand it. It was, however, available when necessary.
I see two ways to go about designing a prohibitively unfun system. First, you could make it baroque and awful, as in the Mind’s Eye Theatre example above. Second, you could make it trivial and boring: e.g., “flip a coin; whoever wins, wins” or, in some cases, “go sit out the next half-hour of the game and then the GM will make a call.” (Which I guess is sort of like the MET option but with less bookkeeping.)
I suspect baroqueness might be the right choice for activities that would be seem thematically appropriate (and thus characters might reasonably have relevant abilities) but undesirable for the particular game, and triviality the way to go for actions that lie further outside the game’s focus.
No doubt when I try this in the future I’ll find the downside of the approach, but right now it looks pretty solid.